Treating hydrocarbon oils



May 15, 1934. w. MfSTRATFORD TREATING HYDROCARBON OILS Filed Nov. 28,1928 2 Sheets-Sheet l May 15, 1934. w. M. STRATFORD TREATING HYDROCARBONOILS Filed Nov. 28, 1928 2 Sheets-Sheet 2 J. R m w w W 8 om @553 xfi M WmN u #8 QEQQI 3 W a g m 5 0M o o 9 3E cu N 3&38 5,35%

Patented May 15, 1934 PATENT OFFICE 1,958,953 TREATING HYDROCARBONOILS-7' William M. Stratford, New York, N. Y., assignor to The TexasCompany, New York, N. Y., a corporation of Delaware Application November28, 1928, Serial No. 322,310

7 Claims.

This invention relates to the cracking of hydrocarbon oils for theproduction of lower boiling products such as gasoline or naphthadistillates.

My invention contemplates subjecting the origd inal charging stock to betreated to a primary cracking operation accompanied with removal ofevolved vapors, the dephlegmation of these vapors to obtain the lightdistillate desired and to form also a higher boiling fraction andfinally the treatin meat of this higher boiling fraction at highertemperatures and pressures than obtain in the primary cracking zone orthe subjection of this fraction to a cracking operation which is notaccompanied with the separate removal of vapor from the secondarycracking zone during the operation.

In one method of operation contemplated by the invention the evolvedvapors from the primary cracking zone are subjected toa dephlegmating orfractionating action so as to form the light distillate desired and ahigher boiling fraction containing constituents the criticaltemperatures of which are below the temperature of the primary crackingzone. There is a disadvantage in returning these constituents to thesame cracking zone from which they have come due to the fact that theirpresence tends to' increase the pressure that it is required to carry insuch cracking zone and, due to the volatility of these constituentsunder the conditions obtaining in the cracking zone, it is difficult tomaintain these constituents within a zone of sufficient temperature forsuflicient time to effect the desired degree of cracking.

' The fraction containing these constituents is therefore, instead ofbeing returned to the original cracking zone, conducted to a secondaryc'facking zone which may be maintained under conditions better suitedfor the conversion of these constituents. Thus the fraction may beconducted to a cracking zone maintained at higher 40 temperatures andpressures than obtain in the primary cracking zone. Furthermore, theinvention contemplates that this fraction containing constituents thecritical temperatures of which are below the temperatures obtaining inthe primary cracking zone may be treated in a cracking zone withoutremoval of vapor during the operation. In this way an original chargingstock, comprising constituents from which a good yield of lightdistillate can be obtained in a cracking operation carried on withdistillation under pressure during the operation, is treated in this wayand the digestion without distillation or the separate removal of vaporduring the operation is applied to the more refractory fraction that isobtained from the evolved vapors of the primary cracking operation.

In a preferred embodiment of the invention the original charging stockis heated to a cracking temperature and subjected to crackingaccompanied with separate removal of vapor in a primary cracking zone,the evolved vapors are passed to a fractionating column from which anoverhead gasoline or naphtha distillate is obtained and also a refluxcondensate which is withdrawn from the tower and forced through aconduit of restricted cross section wherein the oil is heated to ahigher temperature than obtains in the fractionating column andpreferably to a higher temperature than is employed in the primarycracking zone. The oil thus heated is then discharged into an enlargedreaction chamber which is maintained at the desired cracking temperatureand pressure for a sumcient period of time to effect the desiredcracking. The reaction chamber is in the form of a closed converter orautoclave from which there is no separate removal of vapor and theliquid contents of the converter, including such commingled vapors asmay be present, are

directed into the primary cracking and vaporizing zone for distilling ohthe lower boiling products formed in the reaction chamber.

, In order to more fully disclose the invention reference will now behad to the accompanying drawings wherein Figure 1 is a diagrammaticsectional elevation of an apparatus constituting one example and apreferred embodiment of the invention.

Figure 2 is a diagrammatic view illustrating a modification of theinvention.

Figure 3 is a partial sectional elevation showing another modificationofthe invention.

The apparatus thus illustrated includes as elements of the primarycracking zone a charging pump 10, a heating coil 11 and a pressure still12. The charging pump 10 is adapted to draw charging stock from asuitable source and introduce it through a charging line 13 to the -coil11 which is positioned in a furnace 14. A transfer line 15 is providedfor conducting the heated oil from the coil 11 to the still 12. A valve16 is indicated in the transfer line so that if desired the pressure inthe still 12 may be lower than that obtaining in the coil 11. It is tobe understood, however, that suflicient pressure is maintained in thestill 12 to insure that the desired cracking will take place therein andif desired the pressure in the still may be substantially the same asthat in the coil 11. The still is either insulated to prevent loss ofheat or is positioned in a furnace adapted to maintain the desiredcracking temperature. In some 'cases a battery or plurality of stillsmay be used in lieu of the single still shown in the drawings.

The still is equipped with a residue or tar drawoff line 17 and with avapor line 18 which communicates with a dephlegmator or fractionatingcolumn 19. A vapor line 20 conducts vapors from the fractionating columnto a condenser coil 21 and a receiving drum 22 having a valved gasoutlet line 23 and a valved condensate draw-off line 24 is provided forreceiving the pressure distillate. The tower 19 may be a packed tower ora bubble tower or of any suitable design to effect the fractionation orrectification of the vapors evolved from the still 12. Part of thecondensate from the receiver 22 may be pumped back to the top of thetower to serve as a cooling reflux therefor or the tower may be equippedwith cooling coils or a separate reflux condenser or any other suitablemeans for cooling. If desired, the vapor line 18 may be equipped with avalve as illustrated so that the fractionation in the tower 19 may becarried on at a lower pressure thanthat of the still 12, or the valvemay be omitted and the fractionation conducted under substantially thepressure of the still.

The line 25 is provided for conducting reflux condensate from the tower1.9 to the hot oil pump 26 which operates to conduct the refluxcondensate through a line 27 into a coil 28 positioned in a furnace 29,and a transfer line 30 is provided to conduct the oil thus heated into areaction or digestion chamber 31. A line 32 is shown having a valve 33for conducting oil from the reaction chamber 31 into the still 12.

' In practicing the invention the charging stock to the primary crackingzone may constitute any distillate or residuum adapted for treatment forconversion into lower boiling point products. The charge is preferably avirgin stock, that is, an oil which has not been subjected'to anymaterial cracking operation and thus the charge may comprise a. gas oildistillate as obtained from the crude stills and which has not beensubjected to an essential cracking operation. Although a cycle stock,that is, an oil which has been subjected to a prior cracking operationand which has not been converted into the boiling point product desired,may be introduced into the primary cracking zone, it is preferable touse as the charging stock to the primary cracking zone a virgin stock ormixtures of virgin and cycle stocks. Cycle stock may be admitteddirectlyto the secondary cracking zone by the charging line 34 and pump35.

In carrying out the process with the apparatus thus illustrated thevirgin gas oil or other charging stock that it is desired to treat israised to the desired cracking temperature in the coil 11 and passedthence into the cracking and vaporizing chamber 12. The temperature ofthe oil as delivered to the transfer line 15 is ordinarily about 800 to900 F., preferably about 850 to 875 F. A body of cracking and vaporizingoil is maintained in the still 12 under pressures of about 200 to 500pounds pressure, preferably about 400 pounds pressure at temperatures ofabout 750 to 850 F., preferably approximating 825 F. Tar or residue iswithdrawn from the still 12 either continuously or by shots as may bedesired and the evolved vapors pass through the vapor line 18 to thefractionating column 19 wherein they are subjected to fractionation so'as to form a vapor fraction which is removed through the line 20 andwhich is collected in the receiver 22 as a condensate constituting thegasoline or naphtha distillate desired. The reflux condensate whichcollects in the bottom of the tower 19 and which contains constituentsthe critical temperatures of which are below the cracking temperaturemaintained in the still 12 is forced by the hot oil pump 26 through theheating coil 28.

The reflux condensate which collects in the bottom of the tower 19 is atan elevated terriperature, usually at a temperature approximating 700 to750 F. or higher and this hot oil is further heated in the coil 28,preferably to a higher temperature than the temperature maintained inthe still 12. Thus the oil delivered to the transfer line 30 mayapproximate 875 to 1000 F. The heated oil is delivered by the transferline 30 into the reaction chamber 31 wherein a body of oil ismaintained, preferably at higher temperatures an pressures than obtainin the still 12. This reaction chamber or secondary cracking zone isordinarily held at pressures ranging from 600 to 1000 pounds and at atemperature ordinarily only slightly below that maintained in thetransfer line 30. In some cases, if desired, the reaction chamber 31 maybe equipped with a line (not shown) adapted for drawing off a certainamount of tar or residue from the bottom in order to thus prevent anyexcessive deposition of carbon in the chamber but there is nodistillation carried on in this chamber, that is, no separate removal ofvapor as distinct from residual products effected and the contents ofthe chamber 31 that have been subjected to the cracking operation aredirected into the line 32 and passed thence through the pressurereducing valve 33 into the still 12. Although .these products thusdischarged from the reaction chamber or secondary cracking zone may besubjected to fur- 115 ther cracking in the primary cracking andvaporizing zone it may be stated that ordinarily the reaction chamber ofthe secondary cracking zone is held at higher temperatures and pressuresthan the primary cracking zone so that the discharge 120 of constituentsfrom the secondary cracking zone into the first is primarily toaccomplish distillation of the products thus discharged rather than toeffect further cracking.

One method of operation contemplated by the 125 invention includes, ashas been stated, the introduction of cycle stock or oil that has alreadybeen subjected to a cracking operation directly into the secondarycracking zone. In this method of operation a virgin stock or a mixtureof virgin 130 and cycle stock may be introduced by the pump 10 to theprimary cracking zone and a cycle stock introduced by the pump 35 to thesecondary cracking zone, the reflux condensate obtained'from thedephlegmation of vapors from the primary cracking zone being also passedto the secondary cracking zone.

In one modification of the invention the evolved vapors from the primarycracking zone are fractionated into two cuts or fractions besides thatof the gasoline or naphtha distillate, the lighter of these two cutscomprising essentially constituents the critical temperatures of whichare below the temperature obtaining in the primary cracking zone andthis cut is 'conducted to the H5 secondary cracking zone for cracking athigher temperatures and pressures and without separate removal of vaporduring the operation, while the heavier of these two cuts is returned tothe primary cracking zone. Thus in lieu of the single fractionatingtower 19, shown in Figure 1, two towers may be used, as indicated in"Figure 2, the vapor line 18 communicating with the first tower 19a and avapor line 36 extending from the tower 19a to the second tower 19b towhich is connected the vapor line 20. The heavier condensate obtained inthe first tower is withdrawn through the line 25a and pumped by means ofa pump 38 back to the coil 11 for passage with the original chargingstock into the still 12 and the intermediate fraction drawn from thebottom of the second tower and consisting essentially of constituentsthe critical temperatures of which are below the temperature in theprimary cracking zone, is drawn oif through the line 25b to the pump 26and forced into the heating coil 28 and thence into the reaction chamber31.

In another modification of the invention, instead of passing crackedproducts from the reaction chamber 31 into the cracking still 12 theseproducts are directed into a dephlegmator or fractionating tower whichreceives the vapors from the cracking still 12. Two fractionatingtowers, such as shown in Figure 2, may be provided in this method ofoperation, the vapors from the cracking still 12 passing through line18, and the products from the reaction chamber 31 passing through line32 and branch line 321;, to the lower part of the first fractionatingtower 19a. The vapors from the tower 19a pass to the second tower 19band the overhead vapor fraction taken off the tower'19b constitutes thegasoline or naphtha distillate desired while the reflux condensate orbottoms obtained in this tower constitute ,the charge to the secondarycracking zone including the heating coil 28 and reaction chamber 31. Theresidual oil obtained in the bottom of the tower 19a is preferablywithdrawn from the system, as through a line 37. If desired, instead ofhaving two towers a single tower may be employed, as indicated in Figure3, the vapors from the cracking still 12 or primary cracking zone beingdelivered through the vapor line 18 into a tower 190 at a point abovethe point of entry of line 32a which delivers products from the reactionchamber 31 or secondary cracking zone. The charge to the secondaryreaction zone may be drawn off through the line 25b from a pocket 38 inthe tower 190 at a point above the point of entry of line 32a whichintroduces products from the secondary cracking zone.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore, only such limitations should beimposed as are indicated in the appended claims.

I claim:

1. In the conversion of higher boiling hydrocarbon oils into lowerboiling oils, the process that comprises passing fresh clean chargingoil through a heating zone of restricted cross section wherein it israised to a cracking temperature under a pressure of at least 200 poundsper square inch, subjecting the resulting hot oil in a primary crackingzone to cracking temperatures at a superatmospheric pressure of at least200 pounds per square inch to effect cracking and vaporization,subjecting evolved vapors to fractionation to form a vapor fraction ofrequisite boiling point for the light distillate desired and a higherboiling point condensate containing constituents the criticaltemperatures of which are below the cracking temperatures obtaining inthe primary cracking zone, withdrawing this condensate from thefractionating zone, passing condensate .so withdrawn through a zone ofre-- and upwards but without concomitant and sep-' arate removal ofvapor to thereby effect cracking anddigestion, expanding the crackedproducts from said enlarged zone into the primary cracking zone fordistillation and preventing residual products of cracking from enteringsaid heating zone.

-2. In the conversion of higher boiling hydrocarbon oils intqlowerboiling oils, the process that comprises passing the oil undersuperatmospheric' pressure through a zone of restricted cross section tothereby raise the oil to a cracking temperature, directing the heatedoil into a distilling zone wherein a body of oil is maintained atcracking temperatures under a superatmospheric pressure of at least 200pounds per square inch, passing evolved vapors from the distilling zoneto a fractionating zone and subjecting the vapors therein tofractionation to thereby form avapor fraction of requisite boiling pointfor the light distillate desired and a higher boiling condensatecontaining constituents the critical temperatures of which are below thetemperature maintained in the distilling zone, withdrawing condensatefrom the fractionating zone in a heated condition and passing it througha zone of restricted cross section to thereby raise the temperature ofthe oil to a higher temperature than that obtaining in said distillingzone, said higher temperature being from 875 F. to 1000 F., directingthe oil thus heated into an enlarged digestion zone wherein a body ofoil is maintained at a substancomitant and separate removal of vapor,ex-

panding the cracked products from said enlarged zone into saiddistilling zone for distillation and preventing residual products ofcracking from drawn from said primary cracking zone and isolated fromthe process.

4. In the conversion of higher boiling hydrocarbon oils into lowerboiling oils, the process that comprises passing fresh clean chargingoil through a heating zone of restricted cross section wherein it israised to a cracking temperature under superatmospheric pressure,maintaining a body of the resulting hotoil in a primary cracking zone ata temperature of not more than 900 and under a pressure of from 200 to500 pounds per square inch to effect cracking and vaporization,subjecting evolved vapors to fractionation to form a vapor fraction ofrequisite boiling point for the light distillate desired and a higherboiling point condensate containing constituents the criticaltemperatures of which are below the cracking temperatures obtaining inthe primary cracking zone, withdrawing this condensate from thefractionating zone, passing condensate so withdrawn through a zone ofrestricted cross section to thereby heat the oil to a crackingtemperature higher than that obtaining in the primary cracking zone,said higher temperature being from 875 F. to 1000 F., directing the oilthus heated into an enlarged digestion zone and maintaining the oiltherein at a substantially constant temperature higher than thatobtaining in the primary cracking zone and under higher pressures of theorder of 600 pounds and upwards but without concomitant and separateremoval of vapor to thereby effect cracking and digestion, expanding thecracked products from said enlarged zone into the primary zone fordistillation and preventing residual products of cracking from enteringsaid heating zone.

5. In the conversion of higher boiling hydrocarbon oils into lowerboiling oils, the process that comprises passing fresh clean chargingoil through a heating zone of restricted crosssection wherein it israised to a cracking temperature under superatrnospheric pressure,maintaining a body of the resulting hot oil in a primary cracking zoneat a temperature of not more than 900 and under a pressure of from 200to 500 pounds per square inch to efiect cracking and vaporization,subjecting evolved vapors to fractionation to form a vapor fraction ofrequisite boiling point for the light distillate desired and a higherboiling point condensate containing constituents the criticaltemperatures of which are below the cracking temperatures obtaining inthe primary cracking zone, withdrawing this condensate from thefractionating zone, passing condensate so withdrawn through a zone ofrestricted cross section to thereby heat the oil to a crackingtemperature higher than that obtaining in'the primary cracking zone,said higher temperature being from 875 F. to 1000 F., directing the oilthus heated into an enlarged digestion zone and maintaining the oiltherein at a substantially constant temperature higher than thatobtaining in the primary cracking zone, and under higher pressures ofthe order of 600 pounds and upwards but without concomitant and separateremoval of vapor to thereby efiect cracking and digestion, fractionatingcombined cracked products derived from said body and from saidcondensate to form a final desired product and preventing residualproducts of cracking from enter ing said heating zone.

6. In the conversion of higher boiling hydrocarbon oils into lowerboiling oils, the process that comprises subjecting oil in a primarycracking zone to cracking temperatures at superatmospheric pressure toefiect cracking and vaporization, subjecting oil in a secondary crackingzone to cracking at higher temperature and pressure than obtains in theprimary cracking zone, passing vapors evolved in the primary crackingzone to a fractionating zone, directing products from the secondarycracking zone into said fractionating zone at a point below the point ofentry of the vapors from the primary cracking zone, withdrawing acondensate from the fractionating zone at a point above that of theintroduction of the products from the secondary cracking zone andconducting this condensate as charging stock to the secondary crackingzone.

7. In the conversion of higher boiling hydrocarbon oils into lowerboiling oils, the process that comprises subjecting oil in a primarycracking zone to cracking temperatures at superatmospheric pressure to'effect cracking and vaporization, subjecting oil in a secondary crackingzone to cracking at higher temperature and pressure than obtains in theprimary cracking zone, passing vapors evolved in the primary crackingzone to a fractionating zone, expanding products from the secondarycracking zone into said fractionating zone, subjecting the commingledproducts therein to fractionation to form a residual product comprisingunvaporized constituents of the expanded products from the secondarycracking zone admixed with condensate formed in the fractionating zone,an intermediate condensate formed of vapors condensed in thefractionating zone and free from residual constitucuts of said expandedproducts from the secondary cracking zone and a lighter distillate ofrequisite boiling point for the final light distillate desired anddirecting said intermediate condensate as charging stock into thesecondary cracking zone.

WILLIAM M. STRATFORD.

